The invention relates to a shifting arrangement for displacing a selector fork of a multispeed transmission assembly along a selector rod, with a positioning element, mounted to be rotatable about an axis, that is connected to the selector fork, movably mounted on the selector rod, via a drive mechanism that is used to transform the rotational movement of the positioning element into a translational movement of the selector fork along the selector rod, and with a locking device for locking the selector fork in selected actuation positions.
The field of use of such shifting arrangements is multispeed transmissions in which the flow of force is produced via positive clutches, in particular, synchronous clutches. In such transmissions a synchronizer hub is connected rotationally fixed to a transmission shaft. Axially adjacent to the synchronizer hub there is a respective speed change gear, which is rotatably mounted on the driveshaft. Each speed change gear is connected on the side facing the synchronizer hub to a clutch element. Both the clutch element and the synchronizer hubs are provided with outer teeth. The inner teeth of a synchronizer sleeve, which surrounds a synchronizer hub circumferentially, is connected rotationally fixed to it and is displaceable in the axial direction, engage with the outer teeth of the synchronizer hub. To shift a gear, the synchronizer sleeve is displaced in the axial direction until the inner teeth of the sliding sleeve are engaged both with the outer teeth of the clutch element and the outer teeth of the synchronizer hub.
The outer circumference of the synchronizer sleeve is provided with a circumferential groove in which the selector fork positively engages. The selector fork is mounted on one or more selector rods to be axially displaceable. An axial displacement of the selector fork on the selector rod by means of a likewise displaceable positioning element leads to a displacement of the synchronizer sleeve in the direction of a speed change gear, and thus to a shift to that speed. There are also embodiments in which the positioning element, and along with it the selector fork, is rotated about the axis of the positioning element, which likewise leads to a displacement of the synchronizer sleeve along the transmission shaft. In another known embodiment, the selector fork is pivotably mounted a distance away from the positioning element on the synchronizer sleeve by dowel pins on the transmission housing, and is pivoted by the positioning element around the dowel pins for shifting.
Cams are also known for shifting more than two gears sequentially with a single positioning element. The cam, rotatable by means of the positioning element, has one or more recessed control cams in which the cam followers, each interacting with the selector fork, engage. Two synchronizer sleeves can be moved by means of suitable numbers and shapes of control cams. Each of the synchronizer sleeves can connect the synchronizer hub associated with it selectively to one or two speed change gears.
The selector fork is moved relative to the selector rod by means of a positioning element that is linked mechanically, i.e. by cables, rods, lever mechanisms or the like, to a gearshift lever that is manually operated by the driver. In other embodiments, externally powered motors are used for moving the positioning element, which make it possible to automate shifting.
An unintended displacement of the selector fork, for instance as a result of shocks during travel, leads to an unintended frictional engagement or to an unintended loss of frictional engagement between the speed change gear and the transmission shaft. In order to avoid this, it is widely known to equip the positioning element or the selector fork with a locking device that locks it in the desired actuation position.
US 2004/0154425 A describes a shifting assembly for a selector fork that comprises a rotatably mounted gearwheel that can be set into motion by a motor via a worm gear. The gearwheel bears a pin, running parallel to the rotational axis of the gearwheel but offset eccentrically outwards with respect to the axis, that extends into a groove of a selector fork assembly. The selector fork assembly is displaceably mounted on a selector rod and cooperates with the circumferential groove of the synchronizer sleeve. The rotational motion of the gearwheel is thus converted into a translational movement of the selector fork by the pin in the groove of the selector fork assembly. The selector fork is locked in its actuating position only by the motor which in the turned-off state holds the worm gear and the gearwheel meshing with it in position. This has the disadvantage that the motive connection between the selector fork assembly and the gearwheel (i.e., the pin and the groove in the selector fork assembly) must permanently transfer the retention forces, so that it must be constructed sufficiently durably, and nevertheless undergoes permanent wear.
It is proposed in DE 198 33 101 A that a displaceable or pivotable positioning element of a vehicle transmission be engaged by means of a locking element. The positioning element comprises a ramp profile in which a ball of the locking element that is resiliently tensioned against the ramp profile engages. The locking element extends through an opening in the transmission housing up to the positioning element arranged therein. Nevertheless, additional measures must be taken to mount the locking element in the transmission housing. In compact transmission casings there is not necessarily sufficient space to mount the locking element.
DE 103 42 133 A describes a locking device for position fixation of a selector fork of a multistage transmission that can be displaced on a selector rod. The locking device snaps the selector fork, or a hub supporting it on the selector rod, into the selector rod. It is considered disadvantageous that the selector rod must be furnished with characteristics (holes or recesses) with which the locking device can interact. Due to the necessary precision, manufacturing of the selector rod accordingly proves to be elaborate and expensive.